1. Field of the Invention
The present invention relates to electrodes for lithium secondary batteries and lithium secondary batteries using the electrodes.
2. Description of Related Art
The group IV elements of the periodic table, such as Sn, are capable of intercalating and deintercalating Li by electrochemically reacting with Li. For this reason, use of the group IV elements for an active material for lithium secondary batteries has been researched, and it is known that such batteries have remarkably large theoretical capacities. However, a problem with active materials made of the group IV elements has been that they tend to become granulated and pulverized into fine powder with repeated charging and discharging, and peel off from the current collector, resulting in poor cycle performance.
The present applicant has found that good cycle performance is obtained with an electrode in which an alloy thin film composed of a metal that can be alloyed with Li, such as Sn, and a metal that cannot be alloyed with Li, such as Co, is formed on a current collector having an arithmetical mean roughness Ra of 0.1 μm or greater. (See International Publication No. WO 02/25757.) In this electrode, the thin film of the active material is divided into insular structures by the charge-discharge reaction, preventing pulverization of the thin film and thus improving cycle performance.
However, there is a demand for further improvement in the cycle performance of the above-noted electrode.